I had this thought as well. It seems that whenever there should be people, they're missing.

For example, the closest analogue for the Jedi Temple "briefing room" (as far as placement of objects, the hologram, etc.) set in ROTS is the ROTJ scene where the rebels plan the attack on the Death Star 2.

Even though you're focused on just a few people and there are aliens present, it feels like the room is full of people because of all the extras. There's also minor characters like Mon Mothma and General Madine, who would almost definitely have their roles filled by aliens if they were in the prequels.

In a scene that only focuses on two people, Anakin and Obi Wan, it's completely empty other than them. Even though there was supposedly a war briefing that Anakin missed, Obi Wan is the only person there left to turn off the hologram projector. There are Jedi seen in your peripheral vision, but it doesn't feel like the two characters are a part of a larger movement. Between the dialogue taking place on couches and the intrigue taking place in empty rooms, it sucks the warmth out of the movie.

I wouldn't necessarily remove aliens, because it makes sense that the Empire would be xenophobic and try to get rid of them, leading to a more human universe. It's definitely a good idea to add people, though.